Mining is a very special environment that is by its very nature hazardous. Mine shafts are very limited physically, often include wet conditions, and can have explosive gases and dust. The mining industry has a long history of accidents and fatalities. As a result, governmental regulations as well as company policies are geared toward making mining safer for those that enter and work in mines. One governmental agency that regulates mining practice in the United States is the Mine Safety and Health Administration (“MSHA”). MSHA provides regulations as well as enforcement of the regulations. Other countries have similar organizations.
Mining equipment is typically large and requires a significant amount of power. Mining equipment is also typically portable. To provide power to the mining equipment, portable power sources are provided in and around mines. Due to the high power requirements of mining equipment as well as mines having long shafts, often mining power source have voltages that are higher than are typically found in industrial situations. It is not uncommon for the mining power sources to provide power with voltages being about 1 kilo volt (“KV”). In addition, due to the portability of the mining equipment and power sources, often power is provided using flexible cables run without conduit. Due to the high voltages, exposed cables, wet conditions, etc., special consideration must be made for safety of the electrical power systems in mining.
One way to increase safety and reliability of mining power systems is to determine if equipment grounding conductors are in place and properly connected. When equipment grounding conductors are not properly connected, have short circuits, etc., when a fault condition occurs electrical current can flow through the earth surrounding mine shafts as well as through mining equipment. Current flowing in unintended routes create a shock hazard for miners both for fault conditions before overcurrent protection reacts as well as steady state conditions when continuous current flow in unintended paths.
MSHA has provided regulations for monitoring current in grounding conductors. MSHA regulations regarding ground current were changed several years ago. Much of the electrical power system equipment in use today in mines today does not meet current MSHA requirements found in testing standard 30 of the Code of Federal Regulations (“C.F.R.”) section 75 and 30 C.F.R. section 77 with respect to ground current monitoring. While most mining applications include a set of power cables that include a pilot wire for transmitting ground monitor signals, in addition to the phase conductors and equipment grounding conductor, there are many applications without a pilot wire. Typically, such systems include a ground monitor apparatus that uses very old technology.